Mechanically loaded direct air circulation commodity disinfestation chamber

ABSTRACT

A disinfestation treatment chamber for treating fruit, flower and vegetable commodities subject to infestation by quarantine pests. The commodities are disinfested so as to meet quarantine restrictions without adversely affecting the quality of the commodity. The commodity is heated inside of the chamber in hot air having a relative humidity of 30-85% until the temperature of the commodity exceeds the thermal death point temperature of the target pest but is not so high as to adversely affect the quality of the commodity. The temperature of the commodity is held at this temperature until the pest is killed. The commodity is loaded into the treatment chamber in bins onto a low friction conveyor track system which transports the bins from one end of the chamber to the other. The commodities are treated while they are inside of the treatment chamber. After treatment of the commodities, the bins are unloaded using the low friction conveyor track system out of the opposite end of the treatment chamber. The chamber includes a fan/heat exchanger located inside the treatment chamber and positioned under the commodity bins. The space directly above the fan/heat exchanger is left unobstructed during treatment to enhance the airflow through the commodity bins.

The present application is a continuation application of [pending] U.S.patent application Ser. No. 08/825,408 which issued as U.S. Pat. No.5,792,419 on Aug. 18, 1999, filed Mar. 27, 1997, which is a continuationapplication of U.S. patent application Ser. No. 08/589,586, filed Jan.22, 1996, now abandoned, which is a continuation application of U.S.patent Ser. No. 08/123,519, filed Sep. 17, 1993, now abandoned.

FIELD OF THE INVENTION

This invention relates to a postharvest disinfestation treatment chamberwhich is used to ensure that commodities such as fruits, flowers andvegetables are free of pests so as to meet quarantine requirements. Moreparticularly, the present invention relates to heating the commoditieswith hot air under controlled conditions of relative humidity to killall life stages of quarantine pests present in the commodity withoutadversely affecting the quality of the commodity.

BACKGROUND OF THE INVENTION

Certain pests are very destructive to agricultural commodities; thusquarantine restrictions are imposed to ensure that these pests are notdisseminated by export of agricultural commodities which may harborthese pests to areas where the pests do not occur. Illustrative of suchquarantine pests are tephritid fruit flies (Diptera: Tephritidae) suchas the Mediterranean fruit fly, Ceratitis capitata (Wiedemann); theoriental fruit fly, Dacus dorsalis Hendel, and the melon fly, Dacuscucurbitae Coquillet. Fruit flies are among the most destructive insectpests of citrus, deciduous fruits, and vegetables. Tephritid fruit fliesare present in Hawaii and have been shown to spread as larvae or eggs infruits or vegetables shipped from infested areas. Agriculturalcommodities such as papayas, mangos, avocados, citrus, cucumbers, andbell peppers produced in Hawaii that may be infested with fruit fliescannot be shipped to the mainland U.S. or Japanese markets withoutquarantine treatment to ensure that the fruits or vegetables are free offruit flies.

Prior to September, 1984, the standard treatment for papayas wasfumigation with ethylene dibromide (EDB). Subsequent to the cancellationby the U.S. Environmental Protection Agency of the use of EDB as a foodfumigant, the quarantine treatment that was adopted consisted ofselecting papaya fruit of no more than quarter-ripeness as defined bycolor standard values measured with a calorimeter and then immersing thefruit in water at 42 degree(s) C. for 30 minutes followed immediately bya second immersion in water at 49 degree(s) C. for 20 minutes (Couey andHayes, Journal of Economic Entomology, 79:1307-1314 (1986)). Thehot-water immersions are used to destroy the fruit fly eggs and controlpostharvest decay. However, the complete treatment is limited because ofthe ripeness selection and because the water immersions are notsufficiently hot to kill fruit fly larvae inside the fruit. Thistreatment was deregistered as an approved method of quarantine treatmentfor papayas in 1991.

Another quarantine procedure, called the “vapor heat treatment”, useshigh-temperature water-saturated vapor to raise the pulp temperature ofpapaya to 44.4 degrees C. over a 6 to 8 hour period. The fruits are heldat the temperature for 8.75 hours, then cooled immediately after theheating phase to below ambient temperature (APHIS, Plant Protection andQuarantine Treatment Manual, Section III, Part 9, Treatment Procedure,1985). Although this procedure is effective against all fruit fly lifestages, the treatment is time consuming and expensive. Also, scaldingdamage to the fruit may occur. A modified version of the vapor heattreatment, the “quick run-up treatment”, requires heating papayas withsaturated water vapor until the fruit center temperature reaches 47.2degree(s) C., then immediately cooling the fruits (APHIS, CFR AmendmentNo. 85-19, Part 318—Hawaiian and Territorial Quarantine Notices).Although this method takes less time, elaborate facilities are stillneeded and some fruits may be damaged by vapor heat.

Another method of treating fruit for these infestations comprisesheating a fruit or vegetable commodity in hot air under controlledconditions of relative humidity until the temperature of the commodityexceeds the thermal death point temperature of the pest but does notadversely affect the quality of the commodity. The commodity is held atthis temperature until the pest is killed. Then, the commodity iscooled. This disinfestation treatment provides a replacement method tothe prior art methods that use hot water or saturated water vapor andwhich have the disadvantages outlined above.

Using the hot air method, fruit and vegetable commodities subject toinfestation by quarantine pests are disinfested so as to meet quarantinerestrictions without adversely affecting the quality of the commodity.The method involves heating the commodity in hot air having a relativehumidity of 30-80 percent until the temperature of the commodity exceedsthe thermal death point temperature of the target pest, but is not sohigh as to adversely affect commodity quality. The temperature is heldat this temperature until the pest is killed. The method is effectiveagainst all life stages of quarantine pests and is suitable forlarge-scale commercial disinfestation of commodities for movementthrough marketing channels, for example, for disinfestation of papayasof tephritid fruit flies such as the Mediterranean fruit fly, the melonfly and the oriental fruit fly.

Under controlled conditions this method does not adversely affect fruitand vegetable quality such as odor, taste, appearance, ripening,texture, shelf-life or other marketable traits of the commodity. Majoragricultural commodities which can be treated by this method include,but are not limited to, fruits and vegetables such as papaya, mango,starfruit (carambola), atemoya, lychee, eggplant, green peppers, sweetpeppers, hot peppers, cucumbers, avocado and squash.

Disinfestation chambers have been built which employ the differentmethods described above for killing various pests in different fruitsand vegetables. One common chamber in use currently includes a fan,typically centrifugal, housed in its own chamber, separate from thecommodity chamber. Such a chamber was taught by Tsuji et al. in U.S.Pat. No. 4,676,152. In the Tsuji chamber air is drawn in, heated by aheat exchanger, and then blown into the commodity chamber. Uniformairflow in such a chamber has proven difficult to maintain. The airflowcan be reversed by the use of flow dampers. However, such dampers serveto further disrupt the airflow. The external positioning of the fanrelative to the chamber creates heat and air flow losses, as well astemperature variations at different locations within the chamber.

Another known method employs horizontal airflow through the chamber. Inthis type of chamber the fans or ducts are mounted on the side of thechamber and blow the air across the chamber horizontally. Horizontalairflow is not conducive to successfully treating commodities stored inbins.

SUMMARY OF THE INVENTION

A pest disinfestation chamber used to disinfest commodities before theyare exported for resale, the commodities transported in bins, afterharvest, the chamber comprising a conveyor track system for transportingbins of fruit or vegetables from a first end of the chamber to a secondend of the chamber, the conveyor track system coupled to the chamber;and a means for heating and circulating air within the chamber andthrough the bins of commodities, the means for heating and circulatingair coupled to the chamber and positioned inside of the chamber andunder the bins of commodities. The conveyor track system includes a lowfriction track for transporting bins of fruit or vegetables from thefirst end of the chamber to a second end of the chamber. The bins areloaded onto the conveyor track system through a first set of end doorsand unloaded off of the conveyor track system through a second set ofend doors, the first and the second set of end doors providing a sealagainst the ends of the bins during treatment of the commodities. Thesecond set of end doors opening into an insect-free zone. The means forheating and circulating air is comprised of an axial fan and heatexchanger. The means for heating and circulating air is comprised of areversible fan and heat exchanger.

A treatment method for disinfesting a fruit, flower or vegetablecommodity of a quarantine pest, which comprises the steps of: loading aplurality of bins, each bin full of a fruit, flower or vegetablecommodity, into an interior of a disinfestation treatment chamber onto alow friction conveyor track system; heating the commodity inside of theplurality of bins in one or more stages with air having a temperatureabove the thermal death point temperature of a target pest, the airheated and circulated by a fan and heat exchanger positioned under theplurality of bins and inside the interior of the disinfestationtreatment chamber; holding the commodity inside of the plurality of binsat this temperature until the target pest is killed; and unloading theplurality of bins from the interior of the disinfestation treatmentchamber using the conveyor track system. The treatment method furthercomprises the step of placing a temperature probe within the sampledfruit or commodity located in a cold spot in each stack or bin withinthe chamber and measuring the temperature of the cold spot to determinethe temperature distribution of the chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a floor plan of the present invention showing thegeneral arrangement of the commodity bins and the fan/heat exchangers onboth sides.

FIG. 2 illustrates a cut away side section of the present inventionshowing the arrangement of the fan/heat exchanger assembly, commoditybins and the conveyor system.

FIG. 3 illustrates a cut away end section of the present inventionshowing the sealing plates of the conveyor system and the track.

FIG. 4 illustrates the air flow path of the present invention when thehigh pressure air is in the bottom plenum and the air flows from thebottom of the commodity bins, through the perforated commodity binfloors, through the commodity and exiting from the top.

FIG. 5 illustrates the air flow path of the present invention when thehigh pressure air is in the top plenum and the air flows from the top ofthe commodity bins, through the commodity, through the perforatedcommodity bin floors and exiting from the bottom.

FIG. 6 illustrates the main program flowchart of the software used tocontrol the treatment of commodities inside of the chamber.

FIG. 7 illustrates the subroutine flowchart for the subroutine RH usedto control the relative humidity inside the chamber.

FIG. 8 illustrates the subroutine flowchart for the subroutine PID usedto control the air temperature inside the chamber.

FIG. 9 illustrates the subroutine flowchart for the subroutine VIEW usedto display the input/output names and locations.

FIG. 10 illustrates the subroutine flowchart for the subroutine CHECKused to change the temperature offsets and test the output channels.

FIG. 11 illustrates the subroutine flowchart for the subroutine CONTROLused to control the operation of the heat exchanger during treatment ofcommodities inside of the chamber.

FIG. 12 illustrates the subroutine flowchart for the subroutine DATAINused to obtain the data from the temperature probes.

FIG. 13 illustrates the subroutine flowchart for the subroutine DATAOUTused to output the data to control channels.

FIG. 14 illustrates the subroutine flowchart for the subroutine MENUused to display the main menu of the software to allow a user to selectan option.

FIG. 15 illustrates the subroutine flowchart for the subroutinePRINTINTERVAL used to change the time interval that data is sent to aprinter.

DESCRIPTION OF THE PRESENT INVENTION

The present invention is an improved, non-chemical disinfestationchamber. The chamber is intended to kill insect pests including fruitflies in various tropical commodities, such as papayas. The commoditycan be contained in bins or stacked trays or baskets (all hereinafterreferred to as commodity bins) which are loaded into the treatmentchamber. Heated air is then forced through the commodity mass to raiseits internal temperature above that required to kill all stages of thetarget insect.

The present invention uses a fan/heat exchanger assembly installedwithin the treatment chamber to circulate heated air through thecommodity. Chambers of the prior art have positioned the fan(s) and heatexchanger(s) outside the treatment chamber, a practice which aggravatesthe problem of poor heat uniformity within the commodity mass and leadsto insufficient or excessive heating. By contrast, the device of thepresent invention positions the fan assembly inside the treatmentchamber, directly below the track supporting the commodity bins. Thisplacement is intended to reduce heat losses and to promote uniformtemperature distribution within the commodity. Given the narrow windowbetween the temperature required to kill the insect and the temperaturewhich damages the commodity, uniformity is very important to successfulcommercial operation.

The temperatures required to kill insects will vary depending on thetype of insect targeted. The temperature which cannot be exceededwithout damaging the commodity also varies depending on the type ofcommodity to be treated. To illustrate an example of the narrow windowthat the chamber of the present invention must operate within, thetemperature necessary to kill a fruit fly is 47.2° C. and thetemperature that cannot be exceeded without damaging a papaya is 48.5°C. Although the temperature at which damage to the commodity occurs,varies according to fruit type, season and weather conditions, papayasare particularly susceptible to heat damage at temperatures above 48.5°C.

The chamber of the present invention has spaces above and below the binswhich form the plenums for air flow. The commodity bins rest upon anairtight low friction track as well as against a vertical side of thelow friction track forcing the heated air, flowing from the fan, to passthrough the commodity mass within the bins before recirculation back tothe fan. Other prior art chambers use rollers to support and transportthe bins through the chamber. The rollers allow air to leak past thebins and bypass the commodity in the bins. In contrast to the prior art,the low friction track of the present invention prevents air leakagearound the bins and thereby controls proper air flow throughout thechamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A floor plan of the disinfestation chamber of the present invention isillustrated in FIG. 1, a side section is presented in FIG. 2 and an endsection in FIG. 3. The chamber of the present invention includes twoidentical rows of four commodity bins each. The drawing of FIG. 1 showsthe floor plan arrangement of the commodity bins 1 through 8 and thefan/heat exchanger assemblies 10 and 11. The two sides of the treatmentchamber are identical and each side has the capacity to hold fourcommodity bins. Each side has a door 22 and 23 located at each end,opening outward to allow commodity bins to be loaded and unloaded. Thecommodity bins are loaded into the treatment chamber at one end,positioned by the conveyor system for treatment and, followingtreatment, unloaded through the door at the opposite end, forming a flowthrough process in the treatment chamber.

The fan 10 forces air through the heat exchanger 11 into one plenum,depending on the fan's direction of rotation, through the commodity intoa return plenum and back to the fan. Thus, one plenum has higher airpressure and the other plenum has low air pressure. The commodity formsone path between the upper and lower plenums while the fan/heatexchanger 10 and 11 forms the return path. The air is forced through thecommodity due to the difference in air pressure between the two plenums.The fan 10 can be chosen to include the capability to reverse itsdirection of rotation allowing air to be forced upward through thecommodity, as illustrated in FIG. 4, or downward through the commodity,as illustrated in FIG. 5, thus promoting uniform heating within thecommodity mass.

The fan/heat exchanger assembly 10 and 11 circulates the air throughoutthe chamber. The fan/heat exchanger assembly 10 and 11 is placedimmediately below the bin track 12 to allow unimpeded loading andunloading of the commodity bins into and out of the treatment chamber.During treatment the space directly above the fan/heat exchangerassembly is not taken up by a commodity bin and forms part of the upperplenum.

The conveyor is utilized for both loading and unloading of the commoditybins. Each chamber side has its own independent conveyor system. Theconveyor system is composed of two parallel bin tracks 12 lined with alow-friction material, two chain loops 16, two fan sealing plates 15, apush rod 20, six idler sprockets 17, two drive sprockets 14, a driveshaft 13 and a gear reduction motor 9. Loading the empty chamber isaccomplished by positioning the fan sealing plate 15 near the driveshaft 13, loading the commodity bins 8 and 7 on the bin track throughthe end door 23 and partially pushing the commodity bins 8 and 7 intothe chamber using a forklift. The gear reduction motor 9 is activated bypulling a switch and stops automatically when the commodity bin 7,pushed by the fan sealing plate 15, is immediately beyond the fan/heatexchanger assembly 10 and 11. The commodity bins 6 and 5 aresubsequently loaded with a forklift. The commodity bin 6 is preventedfrom being pushed over the fan/heat exchanger assembly 10 and 11 by asecond fan sealing plate.

During treatment, the end doors 22 and 23 are closed and sealed and onlythe air trapped inside the chamber is heated and circulated within thechamber. No air from outside the chamber is pulled into the chamber andno air from within the chamber is released out of the chamber duringtreatment of the commodity.

After treatment, the commodity bin 8 is unloaded by a forklift throughthe end door 22. After the commodity bin 8 is unloaded the commodity bin7 is pushed to the end door 22 by the fan sealing plate 15 where itstops automatically. The commodity bins 6 and 5 are pushed passed thefan/heat exchanger assembly 10 and 11, into a position to be unloaded,using the push rod 20.

In the treatment chambers of the prior art, the commodity bins areloaded onto rollers inside the chamber, and pushed into position by handor by the forklift or a hydraulic ram successively pushing the binsinward. The commodity bins are unloaded by workers pulling them out byhand or by a forklift using a hook on the end of a piece of rope. Thehook must be attached to each bin by a worker who crawls into thechamber. By contrast, in the present invention the commodity bins arealso unloaded off of the conveyor track system by a forklift driver whomerely has to activate a switch from his driver's seat to position thenext bin so that it is ready to lift off of the bin track. For example,the forklift driver can pull the commodity bin 8 out after treatment.The forklift driver can then activate the gear reduction motor 9 fromhis seat, by using any known remote control device, which will thenautomatically position the commodity bin 7 at the opening of the enddoor 23. After unloading the commodity bin 7, the commodity bins 6 and 5can then be positioned by again activating the gear reduction motor 9which uses the push rod 20 to position the commodity bins 6 and 5, sothat they are ready for unloading.

The conveyor system is important in providing an air seal between theupper and lower plenums, ensuring that all the air is forced through thecommodity rather than bypassing it. The bin track 12 is comprised of alow friction material covering a steel support member connected to thechamber wall. The low friction material forms an air seal between thesides of the commodity bins and the chamber walls. Compressible paddingon the inside of both of the end doors 22 and 23 compresses against theoutside commodity bins 5 and 8, forming a seal to prevent air leakagebetween the outer commodity bins and the end doors. The fan sealingplates 15 which extend upward from the bin track 12 prevent air leakagebetween the end of the inner commodity bins 6 and 7 and the fan/heatexchanger assembly 10 and 11.

The use of rollers to facilitate the chamber loading process, as used intreatment chambers of the prior art, creates difficulties in achieving agood air seal between the bins and the chamber walls. A good air sealbetween the bins and the chamber walls will ensure that the heating airdoes not bypass the commodity. One method used in the prior art toalleviate such difficulties consisted of positioning sealing material onthe side of the chamber walls, relying on compression of the sealingmaterial by the commodity bins to maintain the air seal. However, thismethod has drawbacks because the sealing material impedes the loadingand unloading of the bins and will be worn away, over time by thefriction of the passing bins.

The placement of the fan/heat exchanger assembly 10 and 11 inside thetreatment chamber eliminates the heat losses and airflow inefficienciesprevalent in the chambers of the prior art which employ fan(s) and heatexchanger(s) external to the treatment chamber. The interior placementof the fan/heat exchanger assembly 10 and 11 also serves to minimize thevariations of the temperature distribution between the commodity binsand within the commodity in the commodity bins.

The design of the chamber of the present invention also does not use anyducts to circulate the air within the chamber. The ductless constructionof the chamber lowers the construction and operating costs and increasesthe efficiency of the chamber. The commodities themselves, stored in thebins, along with the plenums above and below the fruit, provide thereturn passage for the airflow.

The fan/heat exchanger assembly 10 and 11 can be of any known type offan and heat exchanger, including but not limited to centrifugal, axialor reversible. The fan of the preferred embodiment is both axial andreversible allowing the air flow within the chamber to be reversed.

During treatment of the commodities, the chamber of the presentinvention is controlled by a computer which monitors the temperatureinside the chamber and can increase or decrease the temperature asneeded. A plurality of temperature probes are inserted into commoditysamples distributed within each commodity bin inside the chamber intospots within the chamber which take the longest elapsed time to reachthe fruit center kill temperature called “cold spots.” The cold spotswithin each chamber are determined during a certification process inwhich a relatively large number of commodity probes are distributedthroughout the chamber and monitored by a plurality of computers. Thesecomputers then record the temperature of each probe over the treatmentperiod to identify the location of the cold spots within the chamber.

After the cold spots are determined, during regular operation of thetreatment chamber, a limited number of temperature probes are insertedinto the center of fruit and placed at the cold spots, usually one probeper commodity bin. The temperature measured by each of these probes isthen monitored by the computer to indicate when quarantine conditionshave been satisfied. During treatment, the air within the chamber isgradually heated up to a temperature in the range of 48.5° C. to 48.7°C. causing the center of the fruit to heat up slowly to a temperature of47.2° C. Once the center of the fruit reaches this temperature theinsect is considered to be exterminated and the fruit is then cooled toambient temperature. To avoid potential damage to the commercialqualities of the fruit the center of the fruit should not be heated to atemperature exceeding 48.5° C. In order to reduce the risk of notexceeding a possible damage temperature of 48.5° C., the uniformity ofthe air temperature within the bins of the present invention isrequired. If the temperature of the fruit at the cold spot variesgreatly from the temperature of other fruit in the bin, then it ispossible that while the fruit at the cold spot has not yet reached theinsect death point temperature, fruit that is not at the cold spot willhave exceeded the suspected damage temperature of 48.5° C. and will bedamaged. The chamber of the present invention is designed to createuniformity of temperature throughout the chamber and minimize the lossof fruit from overheating.

The time for treatment in the chamber of the present invention isapproximately four to five hours for papayas. During the first threehours of this treatment the relative humidity of the air inside thechamber is kept in the range of 60-70 percent. During the last hour ofthe treatment the relative humidity of the air inside the chamber israised to 85 percent.

The chamber of the present invention is designed to be installed at apacking house, where the commodities are brought in from the fields,after picking. The chamber can be installed in the middle of the packinghouse with a wall built over the chamber separating the area where thechamber is loaded from the area where the chamber is unloaded. The wallis used to form a barrier between a insect-free zone, where thecommodities are prepared for shipping and the area where the commoditiesare unloaded and prepared for treatment after being brought in from thefields. The treatment chamber forms a disinfestation airlock between thetwo areas so that only one end of the chamber can be open at a time.During the loading of the commodity bins into the chamber only theloading end doors 23 are opened and the opposite end doors 22 remainshut thus preventing insects from the commodities from getting into theinsect-free zone. After treatment, when all the insects have beenexterminated, only the unloading doors 22 to the chamber are open andthe treated fruit is unloaded from the chamber into the insect-free zoneand prepared for shipping. After treatment, the commodity is loaded intosealed containers to prevent reinfestation by insects duringtransportation of the commodity.

The software used to control the treatment chamber of the presentinvention is illustrated in the flowcharts of FIGS. 6-15. FIG. 6illustrates the flowchart of the main program used to control thetreatment of commodities inside the chamber. The main program firstcalls the subroutine MENU, illustrated in FIG. 14, which displays a listof options available and allows a user to select an option from thelist. As soon as the user has selected from the menu the software exitsthe subroutine MENU and calls the necessary subroutine according to theoption chosen by the user.

If the user wants to change the relative humidity within the chamberduring treatment, the subroutine RH, illustrated in FIG. 7, is called.The subroutine RH first looks up the current values stored for therelative humidity inside the chamber during treatment and displays thosevalues. The software then asks the user whether the user wishes tochange the values for relative humidity. If the user enters no, they donot want to change the values, then the values are saved and thesubroutine MENU is called. If the user does want to change the relativehumidity values then the software asks the user whether they wish tochange the time interval. If the user wishes to change the time intervalthen the new time interval is entered and the user is then asked whetheror not they wish to change the upper or lower relative humidity limits.If the user does not wish to change the time interval, they areimmediately asked whether or not they wish to change the upper or lowerrelative humidity limits. If the user does wish to change the upper orlower relative humidity limits the new limits are entered. After the newlimits are entered or if the user did not wish to change the upper orlower relative humidity limits, the current values are displayed and theuser is again asked if they would like to change the relative humidityvalues. If the user enters no, they do not want to change the values,then the values are saved and the subroutine MENU is called. If the userenters yes, that they do want to change the values, then the process isduplicated.

If the user wishes to change the time interval values to be used duringtreatment, the subroutine PID, illustrated in FIG. 8, is called. Thecurrent time interval and proportional integer values are looked up anddisplayed and the user is asked whether or not they wish to change thetime interval values. If the user does not wish to change the timeinterval values or the proportional integer values, they are saved andthe subroutine MENU is called. If the user does wish to change thevalues they are then asked whether they would like to change the timeinterval. If the user wishes to change the time interval then the newtime interval is entered and the user is then asked whether or not theywish to change the proportional integer differential values. If the userdoes not wish to change the time interval they are immediately askedwhether or not they wish to change the proportional integer differentialvalues. If the user does wish to change the proportional integerdifferential values the new values are entered. After the new values areentered or if the user did not wish to change the proportional integerdifferential values, the current values are displayed and the user isagain asked if they would like to change the values. If the user entersno, they do not want to change the values, then the values are saved andthe subroutine MENU is called. If the user enters yes, that they do wantto change the values, then the process is duplicated.

If the user wishes to view the names and location of the inputs andoutputs of the treatment chamber, the subroutine VIEW, illustrated inFIG. 9, is called. The names and locations of the inputs and outputs aredisplayed until the user enters a command to instruct the computer thatthe inputs and outputs do not need to be displayed any longer. Once theuser enters the command to terminate the input/output display control isagain returned to the subroutine MENU.

If the user wishes to change the inputs and outputs, the subroutineCHECK, illustrated in FIG. 10, is called. The subroutine CHECK firstdisplays the data outputs and temperature offsets and then calls thesubroutine DATAIN, illustrated in FIG. 12. The subroutine DATAINmonitors the temperature measured at the inputs and then returns controlback to the subroutine CHECK. The temperature measured at the inputs isthen displayed. The user is then asked if they wish to change thetemperature offsets. If the user does wish to change the temperatureoffsets, the new offsets are entered and the subroutine goes back to thestep where the data outputs were displayed. If the user did not wish tochange the temperature offsets, they are then asked if they wish tochange the data output. If the user does wish to change the data output,the current data outputs are changed and the subroutine DATAOUT,illustrated in FIG. 13, is called. The subroutine DATAOUT outputs thedata and then returns back to the subroutine CHECK at the step where thedata outputs are displayed. If the user did not wish to change the dataoutput they are then asked if they still wish to change the inputs andoutputs. If the user does still wish to change the inputs and outputsthe subroutine DATAIN is called and the process, beginning at that stepis repeated. If the user does not want to change the inputs and outputsthe subroutine MENU is called.

If the user wishes to begin a treatment process within the chamber thedisk file and printer are both initialized and the timer is turned on.While the timer is on the subroutine CONTROL, illustrated in FIG. 11, iscalled every 60 seconds. The subroutine CONTROL first determines thetime that has elapsed and then calls the subroutine DATAIN whichmonitors the temperatures at the inputs and then returns back to thesubroutine CONTROL. The air temperature setpoint is calculated and thenthe air temperature error, using the proportional integer differentialvalues, is calculated. The new pump speed is calculated and then therelative humidity error is calculated, using the upper and lowerrelative humidity values. The steam valve setting is determined and thesubroutine DATAOUT is then called. The subroutine DATAOUT outputs thedata and then returns back to the subroutine CONTROL where the data issaved in a disk file and it is then determined if sufficient time haspassed so that the data should be printed. If the data should beprinted, the data is sent to the printer and control is sent back to themain program. If the data should not be printed then control is sentback to the main program immediately. Between sixty second intervalswhen the subroutine CONTROL is not being called, the main program callsthe subroutine VIEW which displays the names and locations of the inputsand outputs. The data is then displayed and the user is asked if theywould like to run the subroutine MENU, which will give them a list ofoptions. If the user wishes to run the subroutine MENU all of theoptions discussed above will be available except the ability to view thedata inputs and outputs and the ability to change the temperatureoffsets and the data outputs. In addition, the user is able to choose tochange the print interval. The user is also able to end the treatmentrun. If the user would like to end the treatment run, the subroutineDATAOUT is called, the data is output, the timer is turned off and thesubroutine MENU is called.

Once the treatment is done, a cooldown period is entered to allow thecommodity to cool down inside the chamber before the end doors areopened. After the cooldown period is over the commodity bins areunloaded into the insect-free zone and the commodity is prepared forshipping.

It will be apparent to one of reasonable skill in the art that variousmodifications may be made to the preferred embodiment without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

EXAMPLE 1

The following table is designed to show the difference in uniformity andtemperature control between a treatment chamber of the prior art and thetreatment chamber of the present invention. The differences inperformance is illustrated in Table 1, which shows measured temperaturesfor a prior art chamber and for the present chamber during test runs.The prior art chamber includes the fan/heat exchanger assembly on theoutside of the treatment chamber using a duct construction to blow theheated air into the treatment chamber. The bins in this chamber arestacked two high and the air flow is reversed every thirty minutes. Thetest on the prior art chamber was run on Jan. 7, 1993, until all of themonitored fruit had their fruit center temperatures raised to 47.2° C.When the last temperature probe, inside a fruit center, reached 47.2°C., the cooling water was turned on immediately and the temperatures ofall the probes recorded. Thirty six probes were used to measure thetemperature inside of the prior art chamber. These temperatures for theprobes are listed in the table and the mean and standard deviation areincluded at the bottom of the table. The temperatures measured at theend of heating ranged from 47.6° C. to 49.3° C., with the meantemperature equal to 48.43° C., a range of temperatures from 47.63° C.to 49.32° C. and a variance in temperatures of 1.69° C.

The treatment chamber in the present invention was tested on Sep. 15,1993 in exactly the same way as the prior art chamber was tested, exceptthat forty probes were used to measure temperature. Once all of thetemperature probes had reached the temperature of 47.2° C., the coolingwater was turned on and the temperatures of all the probes recorded. Thetemperatures of these probes are listed in a side-by-side comparison tothe measurements taken in the test of the prior art chamber toillustrate the greater uniformity of the treatment chamber of thepresent invention to the chamber of the prior art. The temperatures inthe test of the chamber of the present invention ranged from 47.2° C. to48.7° C., with the mean temperature equal to 48.06° C., a range oftemperatures from 47.2° C. to 48.7° C. and a variance in temperatures of1.5° C. Thus, the temperature distribution of the probes in the chamberof the present invention was less likely to exceed the potential damagetemperature to the extent that the probes of the prior art chamber did.In fact, only one probe exceeded the potential damage temperature of48.5° C. in the test of the present invention. While there was only adifference of 0.37° C. between the mean values of the two tests, thatdifference is very great in the narrow temperature range within whichthe treatment chamber must be operated in.

TABLE 1 Prior Art Chamber Chamber of Present Invention Tested 1/7/93Tested 9/15/93 Probe # Temp. ° C. Temp. ° C. 1 47.81 47.9 2 48.57 47.2 348.48 47.6 4 48.44 47.5 5 48.08 48.0 6 48.19 48.2 7 47.63 48.4 8 48.3848.2 9 49.32 48.3 10 48.33 48.4 11 48.38 47.8 12 48.41 48.5 13 48.6248.2 14 48.49 48.3 15 48.35 48.2 16 48.53 48.3 17 48.83 48.2 18 48.1648.1 19 48.77 47.9 20 48.52 48.3 21 48.67 47.7 22 48.47 47.9 23 48.4147.9 24 48.51 48.0 25 48.75 48.0 26 48.36 48.3 27 49.16 47.8 28 48.0847.6 29 48.44 48.0 30 48.23 47.6 31 48.42 47.9 32 48.12 47.7 33 48.2948.0 34 48.55 48.2 35 48.24 47.9 36 48.52 48.7 37 48.4 38 48.3 39 48.540 48.5 Mean: 48.43 48.06 Range: 47.63-49.32 47.2-48.7 Variance: 1.691.5

We claim:
 1. A pest disinfestation chamber comprising: a. a conveyortrack confined for transporting bins of fruit or vegetables from a firstend of the chamber to a second end of the chamber, the conveyor trackcoupled to the chamber so as to divide said chamber into upper and lowerplenums and so as to provide an air seal between the upper and lowerplenums; and b. an assembly for heating and circulating air within thechamber, said assembly for heating and circulating air coupled to thechamber and positioned inside of the chamber.
 2. The pest disinfestationchamber of claim 1 wherein a first and second set of end doors provide aseal against the ends of said bins during treatment of said fruits orvegetables.
 3. The pest disinfestation chamber of claim 2 wherein saidassembly for heating and circulating air is comprised of an axial fanand heat exchanger.
 4. The pest disinfestation chamber of claim 2wherein said assembly for heating and circulating air is comprised of areversible fan and heat exchanger.
 5. A pest disinfestation device fordisinfesting fruit and vegetables comprising a single chamber having afirst end, a second end, an interior and an exterior, said chambercomprising: a. a friction conveyor track for transporting bins of fruitor vegetables which have been loaded through the first end to the secondend for unloading after treatment inside the chamber, the frictionconveyor track coupled to the chamber so as to divide said chamber intoupper and lower plenums and so as to provide an air seal between theupper and lower plenums; and b. a fan and heat exchanger systempositioned under the conveyor track for heating and circulating airwithin the chamber and through the bins of fruit or vegetables.
 6. Thepest disinfestation chamber of claim 5 wherein the friction conveyortrack forces heated air through the bins and prevents heated air frombypassing the bins.
 7. The pest disinfestation chamber of claim 6wherein a first and second set of end doors provide a seal against saidbins during treatment of said fruits or vegetables.
 8. The pestdisinfestation chamber of claim 5 wherein the fan and heat exchangersystem is comprised of an axial fan and heat exchanger.
 9. The pestdisinfestation chamber of claim 5 wherein the fan and heat exchangersystem is comprised of a reversible fan and heat exchanger.
 10. A pestdisinfestation device comprising a single chamber, said single chambercomprising: a. a roller-free conveyor track for transporting bins offruit or vegetables from a first end of the chamber to a second end ofthe chamber, the conveyor track coupled to the chamber so as to dividesaid chamber into upper and lower plenums and so as to provide an airseal between the upper and lower plenums; and b. a system for heatingand circulating air within the chamber and through the bins of fruit orvegetables, said system coupled to the chamber and positioned inside ofthe chamber and under the bins of fruit or vegetables.
 11. The pestdisinfestation device of claim 10 wherein said roller-free conveyortrack comprises a friction track for transporting bins of fruit orvegetables from the first end of the chamber to a second end of thechamber.
 12. The pest disinfestation device of claim 11 wherein saidroller-free conveyor track forces heated air through the bins andprevents heated air from bypassing the bins.
 13. The pest disinfestationdevice of claim 10 wherein said system for heating and circulating aircomprises an axial fan and heat exchanger.
 14. The pest disinfestationdevice of claim 10 wherein said system for heating and circulating aircomprises a reversible fan and heat exchanger.
 15. A treatment systemfor disinfesting fruit and vegetables, comprising: a. a single chamber;b. a friction conveyor track interior to said chamber and coupled tosaid chamber so as to divide said chamber into upper and lower plenumsand so as to provide an air seal between the upper and lower plenums; c.a fan and heat exchanger system positioned under the conveyor track andin the middle of said conveyor track for heating and circulating airwithin the chamber and through the bins of fruit or vegetables; and d.one or more bins containing fruit or vegetables positioned on saidconveyor track, wherein no bins are positioned directly above said fanand heat exchanger system during treatment.